The present invention relates to a polyester resin composition, more precisely a polyester resin composition which can provide a polyester film having a low minimum stretching temperature and excellent heat shrinkability and flexibility.
Recently, polyethylene terephthalate films have been studied for use in heat-shrinkable labels mainly for PET bottles. It will be beneficial for the recycling of PET bottles, if labels are made of the same kind of resin as the bodies of the bottles. However, although polyethylene terephthalate films are excellent in heat resistance, mechanical properties, transparency and the like, they suffer poor elongation, which makes them likely to be torn, and insufficient shrinkability at a low temperature.
To overcome these problems, polyethylene terephthalate copolycondensated with various dicarboxylic acid components and/or glycol components has been studied. However, such a material has not necessarily provide sufficiently improved heat shrinkability at low temperature. Moreover, it has also been studied to improve flexibility and elongation of the resin by blending various elastomers. However, because addition of polyester elastomers even in a small amount makes the resin white, i.e., opaque, for example, this technique has not been practically used yet.
The object of the present invention is to provide a polyester resin composition which can provide a polyester film having a low minimum stretching temperature, and exhibiting excellent heat shrinkability and flexibility.
To achieve the aforementioned object, the present inventors earnestly conducted studies. As a result, it was found that a polyester resin composition comprising an amorphous polyethylene terephthalate resin in admixture with a particular polyester ether resin at a weight ratio of 97/3 to 50/50 could exhibit excellent properties, and thus the present invention has been accomplished.
That is, according to the present invention, there is provided a polyester resin composition comprising (a) an amorphous polyethylene terephthalate resin and (b) a polyester ether resin in admixture at a weight ratio of 97/3 to 50/50, wherein the polyester ether resin (b) is prepared by copolycondensation of (b1) dicarboxylic acid and/or ester derivative thereof consisting mainly of an aromatic dicarboxylic acid and/or ester derivative thereof, and (b2) diols consisting mainly of a C2-C6 alkylene glycol and a poly(C2-C4 alkylene oxide) glycol, and segments derived from the poly(C2-C4 alkylene oxide) glycol constitute 1 to 30% by weight of the polyester ether resin (b), and the polyester ether resin (b) has a peak temperature of tan xcex4 of 20 to 60xc2x0 C.
According to another aspect of the present invention, there is provided a polyester film which is composed of a blended resin comprising (a) an amorphous polyethylene terephthalate resin and (b) a polyester ether resin in admixture at a weight ratio of 97/3 to 50/50, wherein the polyester ether resin (b) is prepared by copolycondensation of (b1) dicarboxylic acid and/or ester derivative thereof consisting mainly of an aromatic dicarboxylic acid and/or ester derivative thereof, and (b2) diols consisting mainly of a C2-C6 alkylene glycol and a poly(C2-C4 alkylene oxide) glycol, and segments derived from the poly(C2-C4 alkylene oxide) glycol constitute 1 to 30% by weight of the polyester ether resin (b), and the polyester ether resin (b) has a peak temperature of tan xcex4 of 20 to 60xc2x0 c.
Preferably, the aromatic dicarboxylic acid is terephthalic acid.
The C2-c6 alkylene glycol is preferably ethylene glycol or tetramethylene glycol, more preferably tetramethylene glycol.
The poly(C2-C4 alkylene oxide) glycol is preferably polytetramethylene oxide glycol.
The segments derived from poly(C2-C4 alkylene oxide) glycol preferably constitute 3 to 20% by weight of the polyester ether resin (b).
According to embodiments of the present invention, there are provided a polyester resin composition comprising (a) an amorphous polyethylene terephthalate resin and (b) a polyester ether resin in admixture at a weight ratio of 97/3 to 50/50, wherein the polyester ether resin (b) is prepared by copolycondensation of dicarboxylic acid and/or ester derivative thereof consisting mainly of terephthalic acid and/or ester derivative thereof, and diols consisting mainly of tetramethylene glycol and polytetramethylene oxide glycol, and segments derived from the polytetramethylene oxide glycol constitute 1 to 30% by weight of the polyester ether resin, and the polyester ether resin (b) has a peak temperature of tan xcex4 of 20 to 60xc2x0 C.; and a polyester film which is composed of a blended resin comprising (a) an amorphous polyethylene terephthalate resin and (b) a polyester ether resin in admixture at a weight ratio of 97/3 to 50/50, wherein the polyester ether resin (b) is prepared by copolycondensation of dicarboxylic acid and/or ester derivative thereof consisting mainly of terephthalic acid and/or ester derivative thereof, and diols consisting mainly of tetramethylene glycol and polytetramethylene oxide glycol, and segments derived from the polytetramethylene oxide glycol constitute 1 to 30% by weight of the polyester ether resin, and the polyester ether resin (b) has a peak temperature of tan xcex4 of 20 to 60xc2x0 C.
According to the present invention, the amorphous polyethylene terephthalate resin (a) preferably has a glass transition temperature of 50xc2x0 C. or higher.
According to the present invention, the poly(C2-C4 alkylene oxide) glycol preferably has a number average molecular weight of 500 to 6,000.
According to the present invention, the polyester ether resin preferably has a melting point of 200 to 240xc2x0 C.
According to the present invention, the polyester ether resin preferably has a melt viscosity of 500 to 30,000 poises as measured at a temperature of 250xc2x0 C. under a shear rate of 91.2 secxe2x88x921.
According to the present invention, the polyester ether resin preferably has a peak temperature of tan xcex4 of 20 to 60xc2x0 C.
The polyester film of the present invention is preferably a heat-shrinkable film.
The polyester film of the present invention preferably has a heat shrinking ratio of 15% or more along the main shrinking direction, and less than 15% along the direction perpendicular to the main shrinking direction at 70xc2x0 C.
The polyester film of the present invention preferably has a thickness of 3 to 500 xcexcm, more preferably 20 to 200 xcexcm.
Embodiments and methods for practice of the present invention will be explained in detail hereinafter.
The component (a) of an amorphous polyethylene terephthalate resin used for the present invention may be, for example, a polyester resin produced by copolycondensation of a component consisting of terephthalic acid or ester derivative thereof and an ethylene glycol component, together with a component consisting of one or more other dicarboxylic acids or ester derivatives thereof and/or one or more other glycol components, i.e., an amorphous co-PET resin.
Specific examples of the amorphous polyethylene terephthalate resin include, for example, polyester resins produced by copolycondensation of terephthalic acid, ethylene glycol, and a dicarboxylic acid other than terephthalic acid, polyester resins produced by copolycondensation of terephthalic acid, ethylene glycol, and a glycol other than ethylene glycol, polyester resins produced by copolycondensation of terephthalic acid, ethylene glycol, a dicarboxylic acid other than terephthalic acid, and a glycol other than ethylene glycol and the like. One kind of the amorphous polyethylene terephthalate resin may be used alone, or two or more kinds of the resin may be used in combination.
Examples of the aforementioned dicarboxylic acid component other than terephthalic acid include, for example, components consisting of aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, ester derivatives thereof and the like. Mixtures thereof may also be used. As the aromatic dicarboxylic acids, there can be mentioned isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(4,4xe2x80x2-carboxyphenyl)methane, anthracenedicarboxylic acid, (4,4xe2x80x2-diphenyl ether)dicarboxylic acid and the like. As the alicyclic dicarboxylic acid, there can be mentioned 1,4-cyclohexanedicarboxylic acid, 4,4xe2x80x2-dicyclohexyldicarboxylic acid and the like.
Examples of the aliphatic dicarboxylic acid include, for example, adipic acid, sebacic acid, azelaic acid, dimer acids and the like. Preferred examples of the dicarboxylic acid component other than terephthalic acid include, for example, isophthalic acid and ester derivatives thereof. The dicarboxylic acid component in the amorphous polyethylene terephthalate resin preferably comprises 60% by mol or more of aromatic dicarboxylic acid component, more preferably 60% by mol or more of terephthalic acid component in view of mechanical properties and heat resistance.
Examples of the glycol component other than ethylene glycol include, for example, 1,4-cyclohexane dimethanol, propylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, decamethylene glycol, 4,4xe2x80x2-dihydroxycyclohexylmethane, 4,4xe2x80x2-dihydroxycyclohexylpropane, ethylene oxide adducted bisphenol A, polyethylene oxide glycol, polypropylene oxide glycol and the like. Any mixtures thereof may also be used.
The amorphous polyethylene terephthalate resin preferably has a glass transition temperature of 50xc2x0 C. or higher. If the glass transition temperature of the amorphous polyethylene terephthalate resin is lower than 50xc2x0 C., the heat resistance is likely to be degraded. The glass transition temperature of the amorphous polyethylene terephthalate resin is more preferably 60xc2x0 C. or more.
The component (b) of polyester ether resin used for the present invention is a polyester ether resin which is prepared by copolycondensation of (b1) dicarboxylic acid and/or ester derivative thereof consisting mainly of an aromatic dicarboxylic acid and/or ester derivative thereof, and (b2) diols consisting mainly of a C2-C6 alkylene glycol and a poly(C2-C4 alkylene oxide) glycol.
As the dicarboxylic acid (b1), there may be used aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(4,4xe2x80x2-carboxyphenyl)methane, anthracenedicarboxylic acid and (4,4xe2x80x2-diphenyl ether)dicarboxylic acid, and ester derivatives thereof, as well as alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and 4,4xe2x80x2-dicyclohexyldicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid and dimer acids, and ester derivatives thereof and the like. The dicarboxylic acid component preferably comprises 70% by mol or more of aromatic dicarboxylic acid, more preferably 70% by mol or more of terephthalic acid in view of mechanical properties and heat resistance.
As the diol (b2), C2-C20 aliphatic diols, alicyclic diols, bisphenol derivatives and the like may be used in addition to the C2-C6 alkylene glycol and the poly(C2-C4 alkylene oxide) glycol. Examples of the diol (b2) include, for example, tetramethylene glycol, polytetramethylene oxide glycol, ethylene glycol, propylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, decamethylene glycol, 1,4-cyclohexane dimethanol, 4,4xe2x80x2-dihydroxycyclohexylmethane, 4,4xe2x80x2-dihydroxycyclohexylpropane, ethylene oxide adducted bisphenol A, polyethylene oxide glycol, polypropylene oxide glycol, mixtures thereof and the like. These may contain trihydric alcohols such as glycerin and trimethylol propane in an amount of 3% by mol or less of the diol component. If the amount of the trihydric alcohol exceeds 3% by mol, the component may be gelled, and thus it is not preferred. The diol component preferably comprises 70% by mol or more, more preferably 90% by mol or more of the C2-C6 alkylene glycol and the poly(C2-C4 alkylene oxide) glycol.
The amount of segments derived from the poly(C2-C4 alkylene oxide) glycol in the polyester ether resin is 1 to 30% by weight, preferably 3 to 20% by weight, more preferably 5 to 17%, still more preferably 10 to 17% by weight, most preferably 10 to 15% by weight of the polyester ether resin.
If the amount of segments derived from the poly (C2-C4 alkylene oxide) glycol in the polyester resin is more than 30% by weight, transparency of the polyester film becomes lower. Such film cannot produce, for example, labels for PET bottles which provide sufficient aesthetic impression. In the process of producing the film, the stretched film may shrink during storage to produce a deformed label or a label which is not shrinkable to a predetermined size. After the label shrinks on a bottle such as a PET bottle, the label may soften and loosen on the bottle.
The amount of segments derived from the poly(C2-C4 alkylene oxide) glycol in the polyester resin composition is preferably 0.05 to 15% by weight, more preferably 2 to 10% by weight of the composition. If the amount of segments derived from the poly(C2-C4 alkylene oxide) glycol is too small, flexibility and heat shrinkability at a lower temperature of the polyester film becomes poor. If it is too large, heat resistance of the polyester film tends to be degraded.
The number average molecular weight of the poly(C2-C4 alkylene oxide) glycol is preferably 500 to 6,000, more preferably 600 to 2,000. If the number average molecular weight is too small, flexibility of the polyester film becomes insufficient. If the number average molecular weight is too large, compatibility is degraded, and transparency of the polyester film becomes insufficient. The number average molecular weight of a poly(C2-C4 alkylene oxide) glycol is determined by reacting the poly(C2-C4 alkylene oxide) glycol with an excess amount of phthalic anhydride and quantifying unreacted phthalic anhydride to calculate an amount of hydroxyl group per 1 g of the poly(C2-C4 alkylene oxide) glycol.
The polyester ether resin used in the present invention preferably has a melting point of 200 to 240xc2x0 C., more preferably, 200 to 230xc2x0 C., further preferably 210 to 225xc2x0 C. If the melting point of the polyester ether resin is too low, heat resistance of the polyester film tends to be degraded. If it is too high, flexibility of the polyester film tends to be insufficient. The polyester ether resin preferably has a melt viscosity of 500 poises to 30,000 poises, more preferably 1,000 poises to 20,000 poises as measured at 250xc2x0 C. and 91.2 secxe2x88x921. If the melt viscosity is too low, extrusion moldability of the film is degraded, and flexibility of the film becomes insufficient. The polyester ether resin has a peak temperature of tan xcex4 of 20 to 60xc2x0 C., preferably 30 to 60xc2x0 C., still preferably 40 to 60xc2x0 C., as measured by Vibron (automatic dynamic visco-elastometer). If tan xcex4 is too low, heat resistance and mechanical properties of the film tend to be degraded. If it is too high, flexibility and heat shrinkability at a lower temperature of the film tends to become insufficient.
In the present invention, polyester ether resin having a flexural modulus in elasticity of 0.5 to 0.9 GPa can be preferably used.
The amorphous polyethylene terephthalate resin (a) and the polyester ether resin (b) used in the present invention can be produced by conventional polycondensation methods well known to those skilled in the art. For example, for the production of polyester ether, terephthalic acid dimethyl ester can be mixed with tetramethylene glycol and polytetramethylene oxide glycol at a predetermined weight ratio, and subjected to transesterification reaction by heating at a temperature of about 150 to 250xc2x0 C. in the presence of a catalyst such as an alcoholate, chloride or oxide of tin, titanium, zinc, manganese, germanium or the like while methanol is being distilled. Then, polycondensation can be carried out by heating at 200 to 280xc2x0 C. under reduced pressure of 10 mmHg or lower to obtain a polyester ether. In this reaction step, a thermostabilizer and the like may also be added.
In this process, it is also possible to add polytetramethylene oxide glycol first, then perform the transesterification, then add tetramethylene glycol, and thereafter perform the polycondensation. It is also possible to directly polycondense terephthalic acid, tetramethylene glycol and polytetramethylene oxide glycol. Furthermore, a polyester ether having an increased molecular weight can be obtained by the so-called solid state polycondensation method, where resin pellets of the polyester ether obtained by the aforementioned melt state polycondensation are treated by heating at a high temperature of 170 to 210xc2x0 C. under an inert gas flow.
The polyester resin composition of the present invention comprises (a)the amorphous polyethylene terephthalate resin and (b)the polyester ether resin in admixture. The mixing ratio of the amorphous polyethylene terephthalate resin (a) and the polyester ether resin (b) in the polyester resin composition is 97/3 to 50/50 in terms of a weight ratio. An amount of the amorphous polyethylene terephthalate resin exceeding 97% by weight gives insufficient heat shrinkability at a lower temperature, and an amount less than 50% by weight gives insufficient heat resistance. The mixing ratio of the component (a) an amorphous polyethylene terephthalate resin and the component (b) a polyester ether resin is preferably 90/10 to 55/45, more preferably 80/20 to 60/40 in terms of a weight ratio.
Examples of the polyester resin composition of the present invention include, for example, dry blends, melt blends and the like of the amorphous polyethylene terephthalate resin and the polyester ether resin. When dry blends or melt blends are produced, various auxiliaries such as an agent for imparting slipping property, lubricant, antioxidant, and colorant can be blended.
Examples of the agent for imparting slipping property include, for example, inorganic particles such as microparticles of silica, talc, kaolin, and calcium carbonate, organic polymer microparticles such as those of poly(meta)acrylic resin, polystyrene resin, and polytetrafluoroethylene resin, closs-linked microparticles of these organic polymers and the like. These particles preferably have a mean particle diameter of 0.1 to 10 xcexcm. Examples of the lubricant include, for example, calcium stearate, sodium stearate, magnesium stearate and the like.
According to another aspect of the present invention, there is provided a polyester film that is composed of the polyester resin composition of the present invention. The polyester film of the present invention can be produced by molding the aforementioned polyester resin composition. The method for producing the polyester film is not particularly limited, and well-known techniques such as those utilizing T-die film-forming machine, inflation film-forming machine and the like may be used. An unstretched film preferably has a thickness of 60 to 300 xcexcm, and has a tensile modulus of about 2,000 to 22,000 kg/cm2 as measured with a film having a thickness of 25 xcexcm.
In the production of polyester films, stretching process may be employed. Usual stretching methods comprise uniaxial or biaxial stretching after the film forming. While the stretching method is not particularly limited, uniaxial stretching, for example, uniaxial stretching along the direction perpendicular to the extrusion direction (main shrinking direction), is preferred for use in heat-shrinkable labels and the like. The stretching temperature is usually about 60 to 90xc2x0 C., but stretching at a low temperature is preferred for obtaining high heat-shrinkage property. The stretch ratio is preferably about 3 to 5 times, but it is not particularly limited.
The polyester film preferably has a thickness of about 3 to 500 xcexcm, more preferably about 5 to 300 xcexcm, still more preferably about 20 to 200 xcexcm, most preferably about 20 to 100 xcexcm. In the case of a heat-shrinkable film, it is preferred that a prestretched film having a thickness of 60 to 300 xcexcm is stretched to prepare a stretched film having a thickness of 20 to 100 xcexcm.
The polyester film of the present invention is preferably a heat-shrinkable polyester film. Heat shrinking ratio of the polyester film of the present invention is preferably 15% or more, more preferably 17% or more along the main shrinking direction, and less than 15%, more preferably less than 13% along the direction perpendicular to the main shrinking direction at 70xc2x0 C.
The present invention will be explained more specifically with reference to the following examples, which are intended to be mere illustration of the present invention. It will be apparent for those skilled in the art that various alterations, modifications, or improvements can be made on the examples without departing from the spirit of the present invention. Therefore, the scope of the present invention is no way limited by these examples.